A preliminary single channel, high speed, stopped-flow calorimeter has been constructed to evaluate mixing speeds, flow velocities, pressure drops, and thermal detection sensitivity. The system uses a variable speed flywheel and electrically actuated clutch to transfer sufficient energy to the two drive syringes to mix reagent volumes of 200 microliters in 10 milliseconds or less. The inlet tubes from the drive syringes, as well as the mixer and the detection chamber are kept at constant temperature between 25 and 50 deg C. An ultra-fast thermistor (1 ms) is located in the detection chamber to measure the temperature rise during the reaction. The detection chamber also contains a quartz observation tube for optical measurement of the reaction.